Eighty-five places lower down football's food chain Luton Town, sixth in the Conference, did a job on Premier League Norwich City. Eighty minutes of containment, keeping their shape and frustrating their illustrious opponents was followed by a swift break and a clinically executed goal to give them a famous victory.

That the winning goal, made by Stuart Fleetwood and JJ O'Donnell and finished by Scott Rendell, was down to his three substitutes must have made the win even sweeter for Luton's manager, Paul Buckle. His opposite number, Chris Hughton, made substitutions of his own, but Grant Holt, Anthony Pilkington and Wes Hoolohan – Premier League regulars all – failed to make a similar impact.

"It shows you how important a good bench can be," said Buckle. "I don't think it's quite sunk in yet, it was an incredible performance by the players. The most pleasing thing for me was we defended very well and carried a threat of our own throughout. We took great strength from beating Wolves in the third round, we stuck to the same plan, we tried to deny them space, and the players got it right."

Hughton, whose starting XI was packed with fringe players, defended his selection. "I made changes, but I made changes in the third round when we beat Peterborough with a very good performance," he said. "They came with a game plan, we found it very difficult to break them down, the good chances we had we didn't put away, and they caught us with what I suppose was a classic counterattack.

"They're a fit side, an organised side, and the one chance they had they put away. It's going to be a tough few days, but all of that we're going to have to take on the chin. We didn't deserve to lose, but we're in a downward spiral and we have to lift ourselves out of it."

As expected, Hughton had opted to use the players who had steered Norwich to that risibly comfortable victory at Peterborough in the previous round. Elliott Bennett, Simeon Jackson, David Fox and Leon Barnett all started, as did Harry Kane, a 19-year-old forward on a season-long loan from Spurs.

Like Norwich, Luton's priority is very much the league – they came into the game just outside the playoff positions – but with rather less scope to rest players, Buckle's line-up was his first team writ large. They had the encouragement of 4,000 travelling supporters, though, the largest number of away fans at Carrow Road this season, and with Norwich's decision to reduce admission prices ensuring the game was sold-out, there was a pleasingly old-fashioned atmosphere around the stadium.

As a spectacle, however, the opening minutes were distinctly lacking. Both sides were playing 4-4-2, albeit Luton were pressing higher up the pitch, and while Norwich's central midfielders, Fox and Jonny Howson, tried to spread the play, they were not helped by Kane's lack of movement up front. For a 19-year-old, he did not look very fit.

Congestion suited Luton just fine. Norwich began to look to hit deep balls down the flanks for the pacy Jackson and Bennett to run on to, but the Luton defence declined to be pulled out of shape, until shortly before the half-hour mark when Jackson, running on to a long ball, finally got clear. Bearing down on goal from an angle, his shot was at a nice height for the Luton goalkeeper, Mark Tyler, to dive to his right to save, and Andrew Surman's attempted follow-up was blocked.

City went closer soon afterwards, when Surman worked space to pull the ball back from the left. Kane's shot was not cleanly hit but it beat Tyler to his left, only to be kicked clear by left-back Greg Taylor.

Barnett, up for a corner – City's first – then headed against the post. The rebound hit Tyler and came desperately close to crossing the goalline before being scrambled clear.

Hughton replaced Kane with Holt at half-time and the big striker immediately won a header that Jackson, on the turn, volleyed straight at Tyler. Holt looked certain to score when Jackson's cross reached him at the far post on 55 minutes, but Tyler – who began his career at Norwich – pulled off a fine reflex save from the diving header.

Luton were not panicking, though, and nor were they without an occasional threat, as Jon Shaw demonstrated when he drifted a shot over the bar from 22 yards. Hughton threw on Hoolahan and Pilkington, but it was Fleetwood, O'Donnell and Rendell who made the difference.

"We'd dearly love to get a Premier League club in the next round too," said Buckle. "Hopefully it will give the squad some belief, because we weren't hanging on. The club has had some tough days in recent years, and I'm just really pleased for everyone connected to it."